As is well known in the art, a variety of room-temperature curable epoxy resin compositions are prepared by blending various types of epoxy resin, compounding resin and additives which vary widely in nature.
Among the epoxy resins, the mainstream epoxy resins which are used as surface coatings for corrosion prevention and surface protection purposes are bisphenol A type epoxy resins. In general, reactive diluents, plasticizers, solvents and other additives, which are selected depending on the particular application or manner of usage, are added to the bisphenol A type epoxy resins to form compositions having an appropriate viscosity for application.
The curing agents commonly used for such compositions include polyamide amines, polyamine resins, modified polyamine resins and mixtures thereof.
These room-temperature curable epoxy resin compositions are often applied to the surface of concrete, mortar and other structures in situ. Since these compositions have poor adhesion on wet surfaces, concrete and mortar structures must be fully dried prior to application of the compositions, requiring a prolonged working time.
For improving the adhesion of room-temperature curable epoxy resin compositions to wet surfaces, there were proposed several methods including addition of fillers capable of reaction with water (e.g., portland cement, active alumina, and silica alumina), addition of polyamine curing agents in excess of their equivalent, addition of fluorinated surface active agents, modification of amine curing agents, and use of polythiol as a resin component.
Japanese Patent Public Disclosure (Kokai) No. 57-132456 discloses a two-component epoxy resin composition including a specific non-cycloaliphatic epoxy resin, a specific polyamide-amine curing agent and a cement composition.
Japanese Patent Public Disclosure (Kokai) No. 57-195139 discloses a two-component epoxy resin composition including a specific non-cycloaliphatic epoxy resin, a specific polyaminde-amine curing agent, a liquid acrylonitrile-butadiene copolymer and a cement composition.
Some of the compositions formulated according to these proposals, however, are still insufficient in wet adhesion. Some are improved in wet adhesion, but poor in other properties such as fast curing, chemical (mainly acid) resistance after curing, and durability. Some cured coatings are limited in use from a safety aspect since they allow health-hazardous organic components to leach out. For these and other reasons, compositions having satisfactory performance are not available.
The epoxy resins which are base resins of compositions are most often bisphenol A type epoxy resins as previously mentioned. Since these resins are liable to crystallize at low temperatures, compositions based on such epoxy resins tend to become solid, which suggests poor shelf stability and an economic disadvantage. Problems also arise with respect to chemical resistance after curing, durability and safety.
As to the curing agents, polyamide amines which are condensates between dimer acids and polyamines, modified cycloaliphatic polyamines (heterocyclic), and Mannich type polyamines are generally believed to be suitable for application to moistened or wet surfaces of concrete and mortar structures. These curing agents, however, retard drying and adversely affect water resistance after curing. Potential leaching of organic components from cured coatings gives rise to a safety problem.